1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, which are suitable for a broadcasting television camera, a video camera, a digital still camera, a silver halide film camera, and the like.
2. Description of the Related Art
In recent years, a zoom lens having a wide field angle, a high zoom ratio, and high optical performance is required for an image pickup apparatus such as a broadcasting television camera, a silver halide film camera, a digital camera, or a video camera. As a zoom lens having a wide field angle and a high zoom ratio, there is known a positive lead type five-unit zoom lens constituted of five lens units as a whole including a positive refractive power lens unit disposed closest to the object side. As this positive lead type zoom lens, there is known the five-unit zoom lens that is suitable for a television camera, in which a magnification lens unit having functions as a variator and a compensator is constituted of three movable lens units, which move in different loci in a zooming operation (see Japanese Patent Application Laid-Open No. H01-126614 or U.S. Pat. No. 4,874,231, and Japanese Patent Application Laid-Open No. H10-031157 or U.S. Pat. No. 5,808,809).
Japanese Patent Application Laid-Open No. H01-126614 proposes a zoom lens constituted of a first lens unit having positive refractive power, a second lens unit having negative refractive power for magnification, a third lens unit having negative refractive power, a fourth lens unit having positive refractive power, and a fifth lens unit having positive refractive power for imaging. In Japanese Patent Application Laid-Open No. H01-126614, the second, third, and fourth lens units constitute a magnification system. Japanese Patent Application Laid-Open No. H10-031157 proposes a zoom lens constituted of a first lens unit having positive refractive power, a second lens unit having negative refractive power and moving for zooming, a third lens unit having negative refractive power and moving for compensating an image plane variation according to the movement of the second lens unit, and a fourth lens unit having positive refractive power for imaging. Then the second lens unit having negative refractive power for magnification is constituted of a second A lens unit having negative refractive power and a second B lens unit having positive refractive power, so as to constitute the zoom lens by five lens units as a whole.
In the five-unit zoom lens described above, it is important to set appropriate refractive power and move condition in zooming operation of the magnification lens unit in order to obtain wide field angle, high zoom ratio and high optical performance over the entire zoom range. For instance, it is important to set appropriate refractive power and moving locus accompanying magnification of the second and third lens units for magnification, in particular, moving locus and the like in the zoom range from the wide angle end to the intermediate zoom position. If such structures are not set appropriately, it is difficult to realize a small size of the entire system and to obtain a zoom lens having a wide field angle, a high zoom ratio and high optical performance over the entire zoom range.